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Phenology of Shorebird Migration in Western Kentucky
Nicole Ranalli and Gary Ritchison

Southeastern Naturalist, Volume 11, Issue 1 (2012): 99–110

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2012 SOUTHEASTERN NATURALIST 11(1):99–110 Phenology of Shorebird Migration in Western Kentucky Nicole Ranalli1 and Gary Ritchison1,* Abstract - Staging areas along the coasts provide reliable food resources, and shorebirds may use the same stopover locations every year. However, shorebirds use sites opportunistically in the interior of North America because of the transient nature of many habitats. Little is known, however, about the use of wetlands by migrating shorebirds in many areas of the Mississippi Alluvial Valley (MAV), including Kentucky. During 2004 and 2005, we examined the phenology of migration by shorebirds using stopover habitats in Kentucky. From March to October, we surveyed shorebirds in each moist soil unit as well as at other natural and man-made wetlands at each wildlife management area. Species abundance was recorded a minimum of once every 10-day period. We observed 25 species and 12,307 individual shorebirds during our study, with Charadrius vociferous (Killdeer; n = 4134), Calidris melanotos (Pectoral Sandpiper; n = 2912), Calidris minutilla (Least Sandpiper; n = 1138), Tringa melanoleuca (Gmelin) (Greater Yellowlegs; n = 942), and Tringa flavipes (Lesser Yellowlegs; n = 911) being most abundant. We observed nearly 75% more shorebirds during fall migration than during spring migration, possibly because less suitable habitat is available in the fall and shorebirds concentrate in those areas. In addition, shorebird migration extended over a longer period in the fall than in the spring, a pattern that likely results because adults migrate earlier in the fall and juveniles migrate later. Our results provide additional evidence that the MAV provides important stopover habitat for many species of shorebirds during both spring and fall migration. Introduction Migrating shorebirds use stopover sites to renew and store energy to continue migration. Staging areas in coastal regions provide reliable food resources, and shorebirds may use the same stopover locations every year (Myers 1983). However, stopover sites are often used opportunistically in interior North America because of the transient nature of many habitats (Skagen and Knopf 1994). In addition, wet and dry cycles make it difficult for shorebirds to predict the location and availability of food resources and the duration of suitable conditions in inland areas (de Szalay et al. 2000). Most studies of shorebird migration in the United States have focused on major stopover locations, such as Cheyenne Bottoms, KS (e.g., Helmers 1991) or Delaware Bay (e.g., Tsipoura and Burger 1999). However, smaller, less frequently visited sites could prove essential for shorebirds in the future because of unpredictable hydrologic patterns (Skagen and Knopf 1993). Furthermore, shorebirds may increasingly use inland sites rather than coastal areas affected by human disturbance (Lafferty 2001) and climate change (Barlein and Exo 2007). During fall migration, sites throughout the Mississippi Alluvial Valley (MAV) support roughly 500,000 shorebirds representing an estimated 30 species (Loesch 1Department of Biological Sciences, Eastern Kentucky University, Richmond, KY 40475. *Corresponding author - gary.ritchison@eku.edu. 100 Southeastern Naturalist Vol. 11, No. 1 et al. 2000). Historically, habitat for migrating shorebirds in the MAV included extensive mudbars, sandbars, drying oxbows, and sloughs. With the construction of levees and other changes in hydrology, the natural function of such systems has been altered (MAVGCP Working Group 2000), lessening the value of the MAV to many wildlife species (Murray et al. 2009) and changing the abundance and dispersion of refueling sites for shorebirds (Twedt et al. 1998). Little is currently known about the use of the remaining wetlands in western Kentucky by migrating shorebirds. Therefore, our objectives were to determine the species and numbers of shorebirds that use wildlife management areas in western Kentucky as stopover sites, as well as the timing of their migration. Methods We studied shorebird migration at three wildlife management areas in western Kentucky: Ballard-Boatwright Wildlife Management Area (WMA; hereafter, Ballard WMA), Peabody WMA, and Sloughs WMA (Table 1). Sloughs WMA is a 4449-ha area of alternating ridges and sloughs with agricultural fields interspersed. Ballard WMA encompasses 6640 ha of agriculture fields, cypress swamps, oxbow lakes, and upland forest. Peabody WMA is a 19,016-ha area of reclaimed emergent wetlands and mine lands. We conducted shorebird (suborder Charadrii) surveys during the spring (11 March to 20 June) and summer–fall (11 July to 31 October) migration in 2004 and 2005. Methods used for shorebird surveys were taken from the Program for Regional and International Shorebird Monitoring and the International Shorebird Survey (http://www.manomet.org/our-initiatives/shorebird-recovery- project/iss-prism/iss/prism-protocols). Although widely used, these methods can produce biased estimates because no adjustments are made for Table 1. Names, locations, and area of sites surveyed for shorebirds at three wildlife management areas in Kentucky, 2004–2005. WMA Site name Longitude, latitude Area (ha) Ballard Olmstead unit 89°06'39.72"E, 37°05'18.70"N 7 Swan Lake 1 89°08'26.22"E, 37°02'04.70"N 3 Swan Lake 2 89°08'08.20"E, 37°02'00.96"N 5 Ballard Shorebird Unit 89°07'15.98"E, 37°00'08.12"N 8 Mitchell Lake 89°02'45.23"E, 37°09'06.25"N 158 B-2 89°02'01.29"E, 37°08'54.00"N 4 Happy Hollow 89°04'38.61"E, 37°08'44.79"N 26 B-3 89°04'13.26"E, 37°07'52.86"N 3 Peabody Peabody Sinclair Shorebird Unit 87°01'33.58"E, 37°14'27.70"N 1 Slough adjacent to S-7 road 86°59'05.40"E, 37°14'30.05"N 16 Paradise Slough 86°59'15.38"E, 37°14'45.40"N 2 Peabody Holmstead Shorebird Unit 86°55'42.68"E, 37°14'35.88"N 1 Sloughs Slough adjacent to State Route 268 87°47'56.53"E, 37°52'03.94"N 41 Slough adjacent to State Route 136 87°48'01.08"E, 37°51'05.82"N 25 Sloughs Shorebird Unit 87°45'26.22"E, 37°50'51.34"N 7 Muddy slough 87°45'18.62"E, 37°51'00.28"N 32 Hardy slough 87°45'10.47"E, 37°50'54.14"N 9 2012 N. Ranalli and G. Ritchison 101 detectability or variation in stopover duration (i.e., the average length of stay at sites may be longer or shorter than the interval between successive counts). For example, Farmer and Durbian (2006) found that surveys conducted without such adjustments can significantly underestimate the number of shorebirds using stopover sites. Our surveys were conducted at least once during each 10-day period. Because most shorebirds migrate at night and move to roost sites by late afternoon (Skagen et al. 2003), all surveys began during the period from 0700–0900 h, and were conducted on days with wind ≤25 kph and no rain. During surveys, we recorded the species and numbers of each species present at each site. A potential bias associated with shorebird surveys is measurement bias, e.g., the height of vegetation can change during the survey period, and taller plants could limit visibility (Skagen et al. 2003). We attempted to reduce the likelihood of such bias by surveying from as many as three or four locations around each site. Bird identification guides (Peterson and Peterson 2002, Sibley 2000) were used to aid in identification. However, even experienced individuals sometimes have trouble identifying some species (Skagen et al. 2003). As a result, shorebirds were sometimes combined into size (e.g., small shorebirds categorized as “peeps”) or taxonomic categories (e.g., yellowlegs or dowitchers). When large numbers of shorebirds were present and counting individuals was difficult, estimation techniques were used. As suggested by Skagen et al. (2003), the estimation techniques used included counting a small number of birds, e.g., 10 birds, to gain a sense of what 10 birds “look like”, then using this approach to determine what groups of 50, 100, and 1000 birds “look like”. Results During 2004 and 2005, we observed 25 species and 12,307 shorebirds at the three wildlife management areas (Table 2). More species and shorebirds were observed during summer–fall (25 species and 7818 individuals) than during spring (17 species and 4489 individuals) migration, and more shorebirds were observed in 2005 (6689 individuals) than 2004 (5618 individuals; Table 2). We observed 22 species of shorebirds in 2004 and 21 in 2005. Overall, the most frequently observed species were Charadrius vociferous (Killdeer; n = 4134, 33.6%), Calidris melanotos (Pectoral Sandpiper; n = 2912, 23.7%), Calidris minutilla (Least Sandpiper; n = 1138, 9.2%), Tringa melanoleuca (Greater Yellowlegs; n = 942, 7.7%), and Tringa flavipes (Lesser Yellowlegs; n = 911, 7.4%) (Table 2). During spring migration, we commonly observed Pectoral Sandpipers (n = 1052, or 23.4% of shorebirds observed), Greater Yellowlegs (n = 852, or 18.9%), Lesser Yellowlegs (n = 665, or 14.8%), and Charadrius semipalmatus (Semipalmated Plover; n = 512, or 11.4%) (Table 2). During summer–fall migration, the most commonly observed species were Killdeer (n = 3906, or 49.9% of all shorebirds), Pectoral Sandpipers (n = 1860, or 23.8%), and Least Sandpipers (n = 799, or 10.2%) (Table 2). During 2005, we observed fewer Killdeer (n = 1673) than during 2004 (n = 2461). However, several other species were observed in greater numbers in 2005 102 Southeastern Naturalist Vol. 11, No. 1 Table 2. Species and numbers of shorebirds observed during spring (S) and fall (F) migration in 2004 and 2005 at the Ballard, Sloughs, and Peabody Wildlife Management Areas, KY. Ballard Sloughs Peabody 2004 2005 2004 2005 2004 2005 % of Species S F S F S F S F S F S F Total total Charadrius vociferus L. (Killdeer) 10 2010 24 1101 30 293 113 271 19 99 32 132 4134 33.6% Calidris melanotos (Vieillot) (Pectoral Sandpiper) 2 1312 50 389 23 74 975 46 0 17 2 22 2912 23.7% Calidris minutilla (Vieillot) (Least Sandpiper) 0 231 3 235 9 86 261 103 5 71 61 73 1138 9.3% Tringa melanoleuca (Gmelin) (Greater Yellowlegs) 62 24 186 33 97 2 465 22 6 3 36 6 942 7.7% Tringa flavipes (Gmelin) (Lesser Yellowlegs) 198 45 96 127 183 5 180 58 0 2 8 9 911 7.4% Charadrius semipalmatus Bonaparte (Semipalmated Plover) 2 33 34 7 0 7 421 11 0 26 55 0 596 4.8% Calidris alpina (L.) (Dunlin) 0 9 0 5 21 149 336 0 0 46 20 0 586 4.8% Calidris pusilla (L.) (Semipalmated Sandpiper) 0 98 31 35 5 21 20 20 17 55 32 12 346 2.8% Tringa solitaria Wilson (Solitary Sandpiper) 5 58 7 64 4 2 13 21 6 4 3 0 187 1.5% Gallinago delicato Ord (Wilson’s Snipe) 6 0 21 19 0 1 18 36 0 0 0 1 102 0.8% Limnodromus griseus Gmelin (Short-billed Dowitcher) 0 1 9 1 0 0 82 4 0 0 0 0 97 0.8% Actitis macularia L. (Spotted Sandpiper) 1 17 5 20 0 10 6 12 0 1 14 1 87 0.7% Calidris himantopus Bonaparte (Stilt Sandpiper) 0 21 0 32 9 1 2 0 0 0 0 0 65 0.5% Tringa spp.A 1 0 1 0 5 0 42 0 0 0 0 1 50 0.4% Limnodromus scolopaceus Say (Long-billed Dowitcher) 0 0 0 0 0 11 38 0 0 0 0 0 49 0.4% PeepsB 0 0 9 0 22 0 0 0 0 0 0 0 31 0.3% Calidris fuscicollis Vieillot (White-rumped Sandpiper) 0 0 8 1 0 0 8 0 0 0 2 0 19 0.2% Pluvialis dominica (Statius Muller) American Golden Plover 0 0 0 8 0 0 2 0 0 0 0 0 10 < 0.1% Phalaropus tricolor (Vieillot) (Wilson’s Phalarope) 0 1 1 3 0 1 2 0 0 0 0 1 9 < 0.1% Calidris mauri Cabanis (Western Sandpiper) 0 5 0 0 0 0 0 0 0 0 0 3 8 < 0.1% Limnodromus spp.C 0 0 0 3 0 0 4 0 0 0 0 0 7 < 0.1% Himantopus mexicanus Müller (Black-necked Stilt) 0 0 0 3 3 0 0 0 0 2 0 0 5 < 0.1% Calidris bairdii Coues (Baird's Sandpiper) 0 1 0 1 0 0 0 0 0 2 0 0 4 < 0.1% Tryngites subruficollis Vieillot (Buff-breasted Sandpiper) 0 4 0 0 0 0 0 0 0 0 0 0 4 < 0.1% Tringa semipalmata Gmelin (Willet) 0 0 0 0 0 0 0 0 0 4 0 0 4 < 0.1% Calidris alba Pallas (Sanderling) 0 0 0 1 0 0 0 0 0 1 0 0 2 < 0.1% Pluvialis squatarola L. (Grey Plover) 0 1 0 0 0 0 0 0 0 0 0 0 1 < 0.1% Scolopax minor Gmelin (American Woodcock) 0 0 0 1 0 0 0 0 0 0 0 0 1 < 0.1% Total 287 3871 485 2086 411 663 2988 604 53 333 265 261 12,307 , ATringa spp. included Tringa melanoleuca and Tringa flavipes.BPeeps included Calidris minutilla, C. pusilla, C. mauri, and C. fuscicollis. CLimnodromus spp. included Limnodromus griseus and Limnodromus scolopaceus. 2012 N. Ranalli and G. Ritchison 103 than 2004 (Table 2), including Greater Yellowlegs (n = 748 vs. 194), Semipalmated Plovers (n = 528 vs.68), and Least Sandpipers (n = 736 vs. 402). During spring, shorebird numbers peaked from mid-April to mid-May (Fig. 1A). During summer–fall migration, shorebird numbers were highest in Figure 1. Mean number of shorebirds observed per 10- or 11-day survey period at Ballard, Sloughs, and Peabody Wildlife Management Areas in western Kentucky during spring (A) and summer–fall (B) migrations during a two-year period (2004–2005). 104 Southeastern Naturalist Vol. 11, No. 1 late July–early August, but shorebirds were observed through the end of October (Fig. 1B). We found interspecific variation in the timing of peak migration among species of shorebirds observed in the greatest numbers. During the spring, peak migration of Greater and Lesser Yellowlegs occurred during mid-March Figure 2. Mean number of Greater Yellowlegs, Lesser Yellowlegs, Semipalmated Plovers, and Dunlins observed per 10- or 11-day survey period at Ballard, Sloughs, and Peabody Wildlife Management Areas in western Kentucky during spring (A) and summer–fall (B) migrations during a two-year period (2004–2005). 2012 N. Ranalli and G. Ritchison 105 and again in late April and early May (Fig. 2A). Numbers were highest from mid- to late April for Semipalmated Plovers, and from late April through mid- May for Least Sandpipers (Fig. 2A). Numbers of Calidris alpina (Dunlin; Fig. 2A) and Pectoral Sandpipers (Fig. 3A) peaked during early to mid-May; whereas, Killdeer numbers were similar from mid-March through mid-June (Fig. 3A). Figure 3. Mean number of Killdeer, Pectoral Sandpipers, and Least Sandpipers observed per 10- or 11-day survey period at Ballard, Sloughs, and Peabody Wildlife Management Areas in western Kentucky during spring (A) and summer–fall (B) migrations during a two-year period (2004–2005). 106 Southeastern Naturalist Vol. 11, No. 1 During summer–fall migration, several species of shorebirds were observed in similar numbers during the period from mid- to late July through October, including Least Sandpipers (Fig. 3B), Greater and Lesser Yellowlegs (but with a slight peak in early-August; Fig. 2B), and Semipalmated Plovers (Fig. 2B). In contrast, numbers peaked in late July and early August for Killdeer and Pectoral Sandpipers (Fig. 3B), and in mid- to late October for Dunlins (Fig. 2B). Discussion We observed 25 species of shorebirds during our study. Similarly, a previous study indicated that 28 species of shorebirds use the MAV as a migratory corridor (Loesch et al. 2000). Shorebirds observed most often during our study were Killdeer, Pectoral Sandpipers, and Least Sandpipers. Similarly, Killdeer were the most common overwintering shorebird reported in east Tennessee (Laux 2008) and in managed wetlands in the MAV (Twedt et al. 1998). Pectoral Sandpipers were the second most abundant shorebird overall and the most commonly observed shorebird during spring migration. Interior wetlands in North America are thought to be important for calidridine sandpipers during spring migration (Skagen 2006, Skagen et al. 1999). Pectoral Sandpipers concentrate in a relatively narrow corridor extending east from 100°W to the Mississippi Valley (Holmes and Pitelka 1998); fewer typically migrate along the east coast (Clark et al. 1993, Placyk and Harrington 2004). In contrast, during the summer and fall, Pectoral Sandpipers, particularly juveniles, migrate across North America in a wide front (Holmes and Pitelka 1998). However, even during summer– fall migration, an estimated 121,000 Pectoral Sandpipers use the MAV, and were second in abundance only to Least Sandpipers (Loesch et al. 2000). Thus, during migration, particularly spring migration, the MAV and Western Gulf Coast Plain are likely as important to Pectoral Sandpipers as any other region (MAV/ WGCPWG 2000). Least Sandpipers were the third most abundant shorebird in our study, with more observed during summer–fall than spring migration. Least Sandpipers might be the most abundant shorebird in the MAV, with an estimated 151,000 individuals migrating through the MAV during fall migration (Loesch et al. 2000). Our results, and the estimates of Loesch et al. (2000), suggest that the MAV is an important migratory pathway for Least Sandpipers. Greater and Lesser Yellowlegs were the fourth and fifth most common shorebirds, respectively, observed during our study, and both species were observed in greater numbers during spring than summer–fall migration. Lesser Yellowlegs migrate primarily in the interior of North America during spring migration, but are found both on the Atlantic coast and interior during fall migration (Tibbitts and Moskoff 1999). Greater Yellowlegs migrate across much of the Americas during both spring and fall migration (Elphick and Tibbitts 1998), but numbers are generally reduced in interior locations during fall migration (Bent 1927). Overall, we observed nearly 75% more shorebirds during summer–fall migration than during spring migration. More shorebirds were also observed during fall migration than during spring migration in western Tennessee (Short 2012 N. Ranalli and G. Ritchison 107 1999). Floodwaters may create more shallow-water and mudflat habitat for shorebirds in the spring than in the fall, when there is generally less precipitation (Loesch et al. 2000). As a result, shorebirds are likely limited to fewer areas of suitable habitat in the fall, with a greater concentration of birds in those areas contributing to the greater numbers observed. We observed nearly five times as many shorebirds during spring 2005 than during spring 2004. Shorebird habitat in the MAV during spring is dynamic and unpredictable compared to coastal areas (Skagen and Knopf 1994, Brown et al. 2001). Despite flood-control structures, agricultural land is often inundated during the spring (Twedt et al. 1998), creating shorebird habitat in unpredictable locations. The potential increase of foraging habitat throughout the region may disperse shorebirds from managed wetlands. Two of our study areas (Ballard and Sloughs WMAs) were inundated during spring 2004 because of rain and subsequent flooding of both the Mississippi and Ohio rivers; therefore, little mudflat and shallow-water habitat was available. In contrast, water levels were lower during spring 2005, which increased the amount of available habitat. In spring, we observed shorebirds during a 91-day period, with peak numbers occurring during a four-week period from mid-April through mid-May. During summer–fall migration, we observed shorebirds for a longer period (113 days), and with the exception of Killdeer and Pectoral Sandpipers, peaks in numbers of shorebirds during that period were generally less apparent. Similar results, with fall migration of shorebirds occurring during a longer period than spring migration, have been reported by others (Andrei et al. 2006, Smith et al. 1991). Fall migration of shorebirds generally occurs over a longer period because adults migrate earlier in the fall and juveniles migrate later (Colwell et al. 1988). For example, in Canada, male Pectoral Sandpipers moving south from breeding areas arrive in July, most females arrive in late July and into August, and juveniles arrive in September and October (Semenchuk 1992). Similar delays by juveniles in initiating migration have been reported for other species of shorebirds that were observed in the greatest numbers during our study, including Lesser Yellowlegs (Tibbitts and Moskoff 1999), Least Sandpipers (Nebel and Cooper 2008), and Semipalmated Sandpipers (Hicklin and Gratto-Trevor 2010). Among the shorebirds observed in the greatest numbers during our study, Greater and Lesser Yellowlegs exhibited early peaks in the spring (mid-March to mid-April), closely followed by Pectoral Sandpipers (beginning in mid-April). Similarly, Greater and Lesser Yellowlegs and Pectoral Sandpipers were found to be the first shorebirds to appear at stopover sites in Arkansas, first arriving in numbers in mid-March (Smith et al. 1991). All three of these species breed at relatively high latitudes (Greater Yellowlegs: 48–58°N [Elphick and Tibbitts 1998], Lesser Yellowlegs: 51–69°N [Tibbitts and Moskoff 1999], Pectoral Sandpiper: primarily above the Arctic circle at 66.33°N [Holmes and Pitelka 1998]) and initiate spring migration early to permit timely arrival on their breeding grounds. During summer–fall migration, we found that numbers of most species were similar during the period from mid-July through October. However, peak Dunlin migration was later than that of other shorebirds (mid- to late October). Dunlins 108 Southeastern Naturalist Vol. 11, No. 1 are generally one of the last shorebird species to leave the breeding grounds (coastal Alaska and Canada) and, in contrast to most other shorebirds, most adults and juveniles migrate together (Warnock and Gill 1996). In sum, our study areas in western Kentucky provided habitat for several species of shorebirds. The MAV, including Kentucky, may become more important for migrating shorebirds in the future because shorebirds may increase use of inland locations with increasing human disturbance in coastal areas (Lafferty 2001), loss of intertidal habitat resulting from sea-level rise caused by climate change (Galbraith et al. 2002), or with habitat losses in other migratory corridors. 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